Prior to the present invention, various methods were evaluated for treating rock to render the rock more resistant to environmental degradation. There have been many studies and methods of improving the quality of building stone and monuments, and limited study has been devoted to coarse aggregate quality improvement.
One study directed to aggregate improvement is shown by the interim report of May 1977, revised and updated January 1978, report PTI 7707 of the Pennsylvania Transportation Institute of Pennsylvania State University of P. V. Cady, "Upgrading of Poor or Marginal Aggregates for PCC and Bituminous Pavements". Various organic materials were evaluated as treating agents for improving the resistance of aggregate to degradation. Although valuable information has been generated from the aforementioned study, a satisfactory solution to the problem of aggregate degradation resulting from exposure to adverse environmental conditions including air pollution, moisture, or inorganic salt contact has not been found. Improvement has been noted by using organic materials, such as epoxy resins, methyl methacrylate, etc., to treat marginal aggregate, but the degree of aggregate upgrading achieved has not warranted the cost of using such material unless the organics were extensively diluted in polluting organic solvents.
Standard engineering tests can be performed to predict the quality of aggregate. One procedure, for example, has been the magnesium or sodium sulfate soundness test, ASTM C88-76. In many instances, local high quality course aggregate is not available for building construction and must be obtained at a high transportation cost. Various procedures have been used in an attempt to improve the quality of marginal or submarginal rock, for example, argillaceous limestone, highly crystalline limestone and graywacke sandstone to upgrade such material for use in portland cement or bituminous concrete. Procedures of the prior art have been found to be unacceptable because of economic or environmental reasons, or the treated rock failed to survive the magnesium or sodium sulfate soundness test.
Improved results have been achieved as shown by U.S. Pat. No. 4,256,501 of George M. Banino, based on the use of an organic solvent mixture of an organic condensation polymer and an aliphatic polyamine. However, organic solvent can present environmental pollution problems. In addition, the aforementioned aryl condensation polymer, for example, silicone-polycarbonate block polymers can significantly increase the cost of such treatment due to the expense of the starting reactants.
The present invention is based on the discovery that polyelectrolytes, i.e., polymeric substances in which the monomeric units of its constituent macro-molecules possess ionizable groups, for example, polyethylenepolyamine, can be employed in the form of an aqueous solution to treat rock, stone or aggregate in the substantial absence of any unhardened cement, or material with adhesive and cohesive properties which make it capable of binding mineral fragments into a compact whole. As shown by AM Neville, Properties of Concrete, on pages 1-102, Wiley Sons, New York, 1973, the term cement includes hydraulic cement. The degradation resistance of the treated rock has been found to be dramatically improved, particularly if the polyelectrolyte treated rock is further wetted with certain metallic salt solvent solutions. It has been found that treatment of the rock, stone, or aggregate in accordance with the practice of the invention can be accomplished in an economic and non-polluting manner.